When a single crystal of 2,5-bis(4'- methoxybiphenyl-4-yl)thiophene (BP1T-OMe) which is a type of TPCO was high-density photoexcited with a pulsed laser, a pulse-shaped emission with a delay time up to 300 ps was observed at room temperature. Such delayed pulsed emission has been observed in superfluorescence in gas phase and solid-state crystals, and in lasing based on exciton polaritons in inorganic semiconductor microcavities. Although the time-delayed pulsed emission with a delay time up to 300 ps in previous studies is phenomenologically very similar to that of superfluorescence and polariton lasing, it was not clear whether spontaneous coherence can be formed in a macroscopic single crystal resonator (>100 μm) without an external resonator at room temperature, or whether exciton-photon strong coupling can be realized in a single crystal resonator.

  Recently, we have investigated optically pumped lasing characteristics of a single crystal of BP3T which is a type of TPCO, and observed multiple splitting of the emission bands with respect to the amplified spontaneous emission (ASE) bands. Based on the mode structures that appeared in the emission spectra, a dispersion plot of energy vs. wavenumber revealed that the phenomenological Hamiltonian which takes into account cavity photons, 0-0 excitons, and excitons coupled to molecular vibrations reproduced the experimental results very well. This may indicate that exciton-polariton states coupled with molecular vibrations are formed in macroscopic self-cavities. This is the first demonstration of a strongly coupled exciton-photon-molecular vibration state at room temperature.

https://onlinelibrary.wiley.com/doi/10.1002/adom.201900136

https://pubs.acs.org/doi/full/10.1021/acsphotonics.2c00123